A prior art battery charging circuit 1, by way of example useful in cell phone battery charging application, is depicted in FIG. 10. A battery charging source Vcharge 1b is provided with its negative terminal connected to the negative terminal of a battery 1a. The positive terminal of the battery charging source Vcharge 1b is bridged to the positive terminal of the battery 1a with a serial connection of a Schottky diode DS 1f and a power Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) 1c, in this case a P-channel MOSFET, with a built-in body diode 1e and a gate control signal Vcontrol 1d. While in some situations the built-in body diode 1e is advantageous, for certain applications, such as the battery charging application, the body diode 1e can be a problem, as will be explained below. Under normal charging mode, the gate control signal Vcontrol 1d is lowered to turn on the power MOSFET 1c causing a charging current IFORWARD through the Schottky diode DS 1f and the power MOSFET 1c to charge the battery 1a. The charging process can be terminated by raising gate control signal Vcontrol 1d (for example, connecting the gate control signal 1d to the MOSFET 1c source voltage) till the power MOSFET 1c is turned off. However, in the absence of the Schottky diode DS 1f and upon an accidental short circuit of the battery charging source Vcharge 1b, the battery 1a can still be short circuited with a reverse current IREVERSE through the built-in body diode 1e even with the power MOSFET 1c turned off. Hence, the Schottky diode DS 1f also functions as a reverse blocking diode to prevent the battery 1a from an accidental short circuit. While a Schottky diode boasts the advantage of very short switching recovery time, it is remarked that for the application of battery charging the short switching recovery time is not a very important performance parameter. To those skilled in the art other types of diode can be used in lieu of the Schottky diode as well. However, the low forward voltage drop of the Schottky diode 1f is advantageous for energy efficiency in that it allows a correspondingly lower amount of wasted power dissipated from the diode during normal charging of the battery 1a. 
FIG. 11 illustrates a prior art MOSFET-Schottky diode Co-package 2 corresponding to the serial connection of the Schottky diode DS 1e and the MOSFET 1c in circuit 1 of FIG. 10. The MOSFET-Schottky diode Co-package 2 has leads group 2f and leads group 2e for external connection. The Co-package 2 has to provide a Die pad one 2a for seating MOSFET die 2c and a Die pad two 2b for seating Schottky diode die 2d. Additionally, the Co-package 2 has to provide bond wire group 2g and bond wire group 2h for connecting both the Schottky diode die 2d and the MOSFET die 2c to the leads group 2f. The leads group 2e extends from die pad one 2a and die pad two 2b. With two die pads (2a and 2b) and two dies (2c and 2d), the MOSFET-Schottky diode Co-package 2 undesirably incurs a large overall package size and associated high assembly cost and high manufacturing cost. Therefore, it is desirable to integrate the serial connection of Schottky diode DS if and power MOSFET 1c of FIG. 10 into one semiconductor die for reduced package size with a single lead frame and lowered assembly cost and lower manufacturing cost.
FIG. 12 is a copy of FIG. 12A from U.S. Pat. No. 6,476,442, from now on referred to as U.S. Pat. No. 6,476,442. In U.S. Pat. No. 6,476,442 the Schottky Diode is replaced with a Pseudo-Schottky Diode. An N-channel MOSFET is fabricated with its source, body and gate connected together and biased at a positive voltage with respect to its drain. The resulting two-terminal device, referred to as a “pseudo-Schottky mode”, functions like a diode but has a lower turn-on voltage than a conventional PN diode. In particular, FIG. 12 illustrates a cross-sectional view showing the structure of one embodiment of a pseudo-Schottky diode 1200 formed in a lateral configuration. A P-epitaxial layer 1204 is grown upon a P+ substrate 1202 using conventional techniques. A P+ body contact 1206 and an N+ source 1208 are shorted by a metal source/body contact 1218. A gate 1216 is also connected to the source/body contact 1218 into a node labeled S/B/G (A), thus making the source/body contact 1218 the anode of pseudo-Schottky diode 1200. A metal drain contact 1214, which connects to the N+ drain 1212, is the cathode of pseudo-Schottky diode 1200 with its contact node labeled D (K), thus making the drain contact 1214 the cathode of pseudo-Schottky diode 1200. An N-drift region 1210 is located adjacent N+ drain 1212.
Thus, FIG. 13A and FIG. 13B, respectively copied from FIGS. 4A and 4B of U.S. Pat. No. 6,476,442, compare the drain-to-source current Id versus drain to source voltage Vds characteristics of a MOSFET having its gate shorted to its drain in Quadrant I operation with that of a pseudo-Schottky diode (i.e., a device which exhibits the pseudo-Schottky effect) in Quadrant III operation. The curve designated PS relates to the pseudo-Schottky diode, and the curve designated M relates to the MOSFET. In both cases, the gate of the MOSFET is tied to the more positive terminal of the MOSFET. FIG. 4A shows that due to the lower turn-on voltage of the pseudo-Schottky diode, the I-V curve of the pseudo-Schottky diode is shifted towards the origin. FIG. 4B is the same as FIG. 4A but plots the log of Id to afford a wider range of comparison of the currents, particularly in the subthreshold region of drain-to-source voltage Vds. In section A, only leakage current is passing through both the pseudo-Schottky diode and the MOSFET, and therefore the currents are approximately equal. In section B of the graph, the pseudo-Schottky diode has turned on; therefore, the pseudo-Schottky current is much larger than the MOSFET current. In section C, the MOSFET turns on and the body effect disappears so that the currents are once again closer together. It is noteworthy that Id is several orders of magnitude higher in the pseudo-Schottky diode than in the MOSFET when Vds is in the range 0.2-0.6 V.
In U.S. Pat. No. 6,734,715, hereinafter referred to as U.S. Pat. No. 6,734,715, a two terminal semiconductor circuit is described that can replace the semiconductor diodes used as rectifiers in conventional DC power supply circuits. A number of semiconductor circuits that can efficiently supply the DC currents required in both discrete and integrated circuits being operated at low DC supply voltages are disclosed. All of these circuits have a forward or current conducting state and a reverse or non current conducting state similar to a conventional semiconductor diode, but with lower forward on voltage VT and better current handling capabilities. In particular, FIG. 14A and FIG. 14B, respectively copied from FIG. 4 and FIG. 5 of U.S. Pat. No. 6,734,715, are illustrated here. FIG. 14A shows a two terminal device 400 formed by a direct connection 435 between the gate 420 and source 430 leads of an n-channel, asymmetrical, normally off JFET. The source 430 and the drain 410 form the two terminal device that can be represented by the diode equivalent 450. The anode lead 460 of the diode corresponds to the source lead 430 of the JFET, while the cathode lead 470 of the diode corresponds to the drain lead 410 of the JFET. FIG. 14B shows a two terminal circuit 500 formed by the connection of a transformer 505 and an n-channel, asymmetrical, normally off JFET 525. The source 530 and the drain 550 form the two terminal circuit that can be represented by the diode equivalent 570. The anode lead 580 of the diode corresponds to the source lead 530 of the JFET, while the cathode lead 590 of the diode corresponds to the drain lead 550 of the JFET. The transformer primary 510 is connected between the source and drain of the JFET. One terminal of the secondary 520 is connected with a current limiting device 560 in series between it and the gate 540 of the JFET, and the other terminal of the secondary is connected to the source of the JFET. The current limiting device will prevent excessive current between the p-type gate structure and the n-type epitaxial region. The polarity dots 515 on the transformer illustrate the 180 degree phase shift between the transformer primary and secondary potential differences. The transformer is a step-up transformer wherein the secondary voltage is greater than the primary voltage by a factor of N, where N is defined as the ratio of secondary turns to primary turns.
In view of these prior arts, there is an ongoing need of:
replacing a conventional Schottky Diode with new types of diode having improved performance parameters; and
integrating the new diode with a power MOSFET at the semiconductor device die level for reduced package size and cost.